In the coating of structural parts, especially by means of thermal coating methods such as flame spraying, plasma spraying, etc., the thickness of the layer being applied is generally determined after the completion of the coating process. In this case, the layer thickness distribution and the texture of such layers is determined by a polished section analysis of a process control sample. The drawback here is that the layer thickness is always determined only on the mentioned process control sample and not on the actual structural part. This leads to inaccuracies in the determination of the layer thickness. If, furthermore, it is found that the layer thickness is to low, for example, further spraying must be done for the corresponding layer. In many applications, this is not possible, so that the entire coating has to be removed from the part once more and be reapplied. These methods are naturally costly and time-consuming and furthermore constitute a prolonging of the time to produce the coated structural parts.
To overcome these disadvantages, DE 44 25 187 A1 proposes a device and a method for measuring of layer thicknesses of the aforementioned kind. Here, the layer thickness or the layer thickness distribution is measured directly on the structural part immediately during or after the coating process. For this, two path length measuring devices are used, using laser triangulation on the one hand to measure the diminishing distance between the surface of the layer being applied and a first path length measuring device. On the other hand, a second path length measuring device is used to determine the distance of this device from an uncoated reference surface of the structural part. In this way, one can allow for measurement inaccuracies, such as those caused by expansion of the structural part due to the heat of the coating process. The reference surface can be, for example, the uncoated back side of the structural part. With the known device and the corresponding known method it is possible to measure the thickness of the sprayed-on layer with an accuracy in the micron range.
The problem of the present invention is to provide a device of the aforementioned kind that leads to a further improvement of the measurement accuracy compared to the known devices.
A further problem of the present invention is to provide an aforementioned method that has a higher measurement accuracy than the known measurement methods.